Power cutter

ABSTRACT

A power cutter comprising: a housing  2;  an engine  24  mounted within the housing  2;  a support arm  7  mounted on the housing and which projects forward of the housing; a blade mounting mechanism rotatably mounted on the end of the support arm and which is capable of being rotationally driven by the engine  24  when the engine is running; a cutting blade having a circular central hole and which mounts on and is rotationally driven by the blade mounting mechanism; a liquid fuel aeration mechanism  126  to generate aerated fuel for the engine; an air intake  314  for the provision of air for the liquid fuel aeration device  126;  an air filtration mechanism  316  to filter the air drawn in from the air intake for the liquid fuel aeration mechanism; a fuel tank  124  for providing fuel to the liquid fuel aeration mechanism; and an exhaust  146  through which the exhaust gases generated by the operation of the engine are expelled; wherein the blade mounting mechanism comprises: a spindle  70  rotatably mounted on the support arm and which is capable of being driven by the engine  24,  an adaptor  90  upon which is mounted the cutting blade, which adaptor is mounted on surrounds the spindle, the adaptor  90  having along its length a plurality of radial support surfaces  98; 100  which are each concentric with the spindle  70,  each having a different radius; a clamping mechanism  96, 92,86  capable of axially and angularly locking the cutting blade to the spindle  70;  wherein, when the blade  10  is mounted on the adaptor  90,  the central hole of the blade  10  mounts on a corresponding sized radial support surface  98; 100  of the adaptor  90  so that the axis of rotation of the blade  10  is substantially co-axial with that of the spindle  70.

FIELD OF THE INVENTION

The present invention relates to a power cutter.

BACKGROUND OF THE INVENTION

A typical power cutter comprises a housing in which is mounted a twostroke internal combustion engine. Attached to the side of the housingis a support arm which extends forward of the housing. Rotatably mountedon the end of the support arm is a cutting blade, usually in the form ofa grinding disk. The motor is drivingly connected to the cutting bladevia a drive belt. The rotary output of the engine rotatingly drives thecutting blade via the drive belt. The drive belt is driven via acentrifugal clutch which enables the out drive spindle of the engine todisengage from the belt when the engine is running at a slow speed, toallow the engine to continue running, whilst disengaging any drive tothe cutting blade to allow the blade to be stationary.

Also mounted in the housing is a petrol tank which provides petrol forthe engine and an oil tank, which provides lubricating oil to mix withthe petrol, to lubricate the engine, to provide a petrol/oil mixture.The petrol and oil mixture is fed into the engine via a carburetor, alsomounted within the housing, which creates an aerated petrol/oil mixture,to power the engine.

Mounted on the rear of the housing is a rear handle for supporting thepower cutter, which contains a trigger switch for accelerating theengine upon depressing. Depression of the trigger switch causes more ofthe aerated petrol/oil mixture to be injected into the engine from thecarburetor which in turn causes the speed of the engine to accelerate.

GB2232913, WO2005/056225 and U.S. Pat. No. 5,177,871 show such powercutters.

BRIEF SUMMARY OF THE INVENTION

Cutting blades for use with power cutter are made from a fiat sheet ofmaterial, typically metal, and have a circular outer circumference. Thecircular outer edge comprises either teeth or other cutting elements,such as diamonds, to form a radial cutting edge. A circular central holeis formed at the centre of the blade which is used to mount the bladeonto a drive spindle. The size of the diameter of cutting blades vary.However, as the size of the outer diameter increases, the size of thediameter of the central hole in the middle of the blade also increases.It is desirable for a power cutter to be able to use a range of sizes ofcutting blades with varying sizes of central hole. In order for it to doso, it needs to be able mount blades having differing sized centralholes. The present invention provides a power cutter which is able to doso.

A power cutter comprising:

a housing;

an engine mounted within the housing;

a support arm mounted on the housing and which projects forward of thehousing;

a blade mounting mechanism rotatably mounted on the end of the supportarm and which is capable of being rotationally driven by the engine whenthe engine is running;

a cutting blade having a circular central hole and which mounts on andis rotationally driven by the blade mounting mechanism;

-   -   a liquid fuel aeration mechanism to generate aerated fuel for        the engine;    -   an air intake for the provision of air for the liquid fuel        aeration device;    -   an air filtration mechanism to filter the air drawn in from the        air intake for the liquid fuel aeration mechanism;    -   a fuel tank for providing fuel to the liquid fuel aeration        mechanism; and    -   an exhaust through which the exhaust gases generated by the        operation of the engine are expelled;

wherein the blade mounting mechanism comprises:

a spindle rotatably mounted on the support arm and which is capable ofbeing driven by the engine,

an adaptor upon which is mounted the cutting blade, which adaptor ismounted on surrounds the spindle, the adaptor 90 having along its lengtha plurality of radial support surfaces which are each concentric withthe spindle 70, each having a different radius;

a clamping mechanism capable of axially and angularly locking thecutting blade to the spindle;

wherein, when the blade is mounted on the adaptor, the central hole ofthe blade mounts on a corresponding sized radial support surface of theadaptor so that the axis of rotation of the blade is substantiallyco-axial with that of the spindle.

BRIEF DESCRIPTION OF THE DRAWINGS

Two embodiments of the invention will now be described with reference toaccompanying drawings of which:

FIG. 1 shows a perspective view of the power cutter from a first side;

FIG. 2 shows a side view of the power cutter from a second side;

FIG. 3 shows a sketch of a horizontal cross section of the belt driveand support arm;

FIG. 4 shows a sketch of the forward and rearward sections of thesupport arm;

FIG. 5 shows a sketch of a horizontal cross sectional view of theconnection between the rearward and forward sections of the support arm;

FIG. 6 shows the belt tensioner;

FIG. 7 shows a computerized drawing of the forward section, drivenwheel, blade and blade guard;

FIG. 8 shows a computerized drawing of the blade and blade guard fromthe opposite direction to that shown in FIG. 7;

FIG. 9 shows a computerized drawing of a close up the blade and bladeguard;

FIG. 10 shows a computerized drawing of a close up the blade and bladeguard without the holding nut;

FIG. 11 shows a computerized drawing of a close up the blade and bladeguard without the first support disk;

FIG. 12 shows a computerized drawing of forward support with the bladeguard;

FIG. 13 shows a computerized drawing of a cut away view of the rotarysupport mechanism from the side with the adapter in the first position;

FIGS. 14 and 15 show computerized drawings of a cut away views of therotary support mechanism from the side with the adapter in the secondposition;

FIG. 16 shows a cut away view of the blade support;

FIG. 17 shows a computerized drawing of a cut away view of the rotarysupport mechanism from a first perspective;

FIG. 18 shows a computerized drawing of a cut away view of the rotarysupport mechanism from a second perspective;

FIG. 19 shows a sketch of the vertical cross section of the body of apower cutter;

FIG. 20 shows a perspective view of the fuel cap;

FIG. 21 shows an exploded view of the fuel cap from a first side;

FIG. 22 shows an exploded view from a second side;

FIG. 23 shows a sketch of a vertical cross section of the part of thepower cutter with the air filter;

FIG. 24 shows a computer generated drawing of the filter;

FIGS. 25 and 26 show sketches of the cleaning action of the filter;

FIGS. 27 to 29 show more computer generated drawings of the filter; and

FIG. 30 shows a second embodiment of an air filtration system.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, the power cutter comprises a body 2 in whichis mounted a two stroke internal combustion engine 24, a front handle 4,a rear handle 6, a support arm 7, a cutting blade 10, rotatably mountedon the support arm 7 and driven by the engine 24 via a rubber belt 26and a blade guard 22. A starter 12 is provided to activate the engine24. A plastic cover 19 covers the out side of the support arm 7 as shownin FIG. 2.

Referring to FIG. 3, the support arm 7 comprises two sections, a forwardsection 8 and a rearward section 20. The rearward section 20 is madefrom cast iron and is rigidly attached to the side of the gear housing32 using bolts (not shown). The forward section 8 is made of cast ironand is slideably mounted on the rearward section 20. The forward sectioncan slide in the direction of Arrow A. The method by which the forwardsection 8 is slideably mounted on the rearward section 20 is describedin more detail below.

The engine 24 has an output shaft 28 on which is mounted a drive wheel30 for the rubber belt 26. The output shaft drives the drive wheel 30via a centrifugal clutch (not shown) in well known manner. A drivenwheel 32 is rotatably mounted on the end of the forward section 8 of thesupport arm. The driven wheel 32 is connected to the cutting blade 10which is also mounted on the forward section 8 as described below. Thebelt 26 passes around the rearward section 20, between the two wheels30, 32 to transmit the rotation of the engine to the cutting blade 10.The purpose of enabling the forward section 8 to slide in relation tothe rearward section 20 is to enable the belt 26 to be tensioned asdescribed below. A hub 16 covers the drive wheel 30.

The interconnection between rearward and forward sections of the supportarm 7 will now be described with reference to FIGS. 3, 4, 5 and 6.

Referring to FIGS. 3 and 4, the rearward section 20 comprises twoelongate slots 40 formed through the width of the rearward section 20.The elongate slots 40 are aligned with each other, are of equal lengthand run lengthways along rearward section 20 of the support arm. Formedthrough the forward section 8 are two corresponding holes 46. The partof the forward section 8 with the holes 46 is located alongside of thepart of the rear section 20 with the elongate slots 40 so that the holes46 align with a corresponding slot 40. A bolt 42 passes through eachhole 46 and corresponding slot 40. A nut 44 is screwed onto the bolt 42to sandwich the rearward and forward sections together and hold them inplace using friction. The slots 40 enable the bolts 42, and hence theforward section 8, to slide relative to the rearward section 20.

In order to slide the rearward section 20 relative to the forwardsection 8, the nuts 44 are slackened so that the two can move relativeto each other. The forward section 8 is then slid (using the belttensioner described below) to the desired position, and then the nuts 44are tightened to sandwich the rearward section 20 to the forward section8 to prevent movement between the two.

The forward and rearward interconnection mechanism is designed so thatthe forward section 8 can be located on either side of the rearwardsection 20 as shown in FIG. 2. In normal operation, the forward section8 is located on the same side of the rearward section 20 as the engine24. This is indicated as position B. In this position, the cutting blade10 is located closer to the central axis of the power cutter. However,it is sometimes desirable to have the cutting blade located towards theedge of the body 2 to enable it to cut near to a wall. The forwardsection 8 can then be moved to the other side of the rearward section 20and be rotated through 180 degrees about the longitudinal axis 48 of theforward section 8 as indicated by Arrow D to the position C. In bothorientations, the driven wheel 32 locates in the same position so thatit can be driven by the belt 26.

The belt tensioner will now be described with reference to FIGS. 4, 5and 6

Referring to FIGS. 5 and 6, the belt tensioner comprises a metal plate50 having two holes 46 through which the bolts 42 pass as seen in FIG.4. The position of the plate 50 is fixed by the position of the bolts42. Formed on the metal plate 50 are two hoops 52 which form apertureswhich are aligned. The shaft of an elongate bolt 54 passes through thehoops 52. The elongate bolt 54 can freely rotate and axially slidewithin the hoops 52. Threadedly mounted onto the bolt 54 is a nut 56. Aspring 58 is sandwiched between the nut 56 and one of the hoops 52. Thespring 58 prevents the nut from rotating. Therefore, as the bolt 54 isrotated, the nut 56 travels along the length of the bolt 54 in adirection dependent on the direction of rotation of the bolt 54. Theposition of the nut 56 is fixed relative to the hoop 52 by the spring58. A stop 60 is integrally formed on the rearward section 20 of thesupporting arm.

In order to tension the belt 26, the elongate bolt is rotated so thatthe nut moves towards the head 62 of the bolt 54. As its position isfixed by the spring 58, the nut remains stationary relative to the hoop52 causing the bolt 54 to axially move within the hoops 52 so that theend 64 of the bolt 54 approaches the stop 60. Upon engagement of thestop 60, the end 64 and hence the bolt 54, can not move further andtherefore the nut begins to move. The movement of the nut causes thespring 58 and hence the hoop 52 to move towards the head 62 of theelongate bolt 54. This in turn results in the plate 50, the two bolts 42and the forward section 8 to move with the nut 56, the bolts 42 slidingwithin the two slots 40. However, when the belt 26 becomes tight, theforward section 8, and hence the bolts 42 and plate 50 are preventedfrom moving further. However, if the elongate nut 54 is further rotated,the nut 56 will continue to travel along its length. Therefore, thespring 58 becomes compressed, applying a force onto the hoop, and henceplate 50, which in turn transfers it to the forward section 8. Thistensions the belt 26. The more compression of the spring 58, the moreforce is applied to the belt 26. An indicator 66 is added to the plate50 to show when the amount of the compression of the spring 58 issufficient to apply the correct amount of force to the belt 26.

The blade mount on the forward section 8 will now be described.

Referring to FIG. 7, the driven wheel 32 is rotatably mounted on theforward section 8. The driven wheel 32 is drivingly connected to thecutting blade 10 via a spindle 70 as will be described in more detailbelow. The blade guard 22 is pivotally mounted around the spindle 70 aswill be described in more detail below. A grasp 72 is rigidly attachedto the blade guard 22 which can held by an operator in order to pivotthe blade guard 22.

FIGS. 12 to 18 show the mechanism by which the forward support 8rotatably supports the cutting blade 10.

Referring to FIGS. 17 and 18, the driven wheel 32 is rigidly attached tothe spindle 70 via a flanged nut 74. Rotation of the driven wheel 32results in rotation of the spindle 70. The spindle 70 is mounted in theforward section 8 using two ball bearing races 76, each comprising aninner track 78 rigidly connected to the spindle 70, an outer track 80rigidly connected to the forward support 8, and a set of ball bearings82 sandwiched between the two tracks 78, 80 which allow the outer track80 to rotate relative to the inner track 78.

Formed along a part of the length of the spindle 70 are two flatsurfaces 84 (see FIG. 16). A second support disk 86 comprises a centralhole which is predominantly circular with the same diameter of thespindle 70, but with two flat sides which correspond in dimensions tothe flat surfaces 84 of the spindle 70. The second support disk 86 ismounted on the end of the spindle 70 and abuts against shoulders 88 onthe spindle 70 formed by the two flat surfaces 84. The flat surfaces 84ensure that the second support disk is rotationally fixed to the spindle70 so that rotation of the spindle 70 results in rotation of the secondsupport disk 86.

An adaptor 90 (described in more detail below) is mounted on the spindle70. The adaptor can freely rotate about the spindle 70. The cuttingblade 10 is mounted on the adaptor 90.

A first support disk 92 comprises a central hole which is predominantlycircular with the same diameter of the spindle 70, but with two flatsides which correspond in dimensions to the flat surfaces 84 of thespindle 70. The first support disk 92 is mounted on the end of thespindle 70 and abuts against the cutting blade 10. The flat surfaces 84ensure that the first support disk 92 is rotationally fixed to thespindle 70 so that rotation of the spindle 70 results in rotation of thefirst support disk 86.

A threaded hole 94 is formed in the end of the spindle 70 (see FIGS. 10to 12). A second flanged nut 96 is screwed into the hole 94. The flangeof the nut 96 pushes the first support disk 92 against the blade 10which in turn pushes the blade 10 against the second support disk 86.The blade 10 becomes sandwiched between the two support disks 86, 92.Rotation of the support disks 86, 92 by the spindle 70 results inrotation of the blade due to the frictional contact of the blade 10being sandwiched between the two disks 86, 92. By frictionally drivingthe blade 10, it allows rotational movement of the blade 10 relative tothe spindle 70 if the blade becomes snagged during the operation of thepower cutter.

The automatic blade support adjustment mechanism will now be described.

Cutting blades of different sizes can be used. Different sized cuttingblades 10 have different sized holes in their centres through which thespindle 70 passes. It is intended that the present power cutter will beable to fit cutting blades 10 having two different sizes of hole throughtheir centres. This is achieved by the use of the adaptor 90.

Referring to FIGS. 17 and 18, the adaptor is mounted on the spindle 70between the two support disks 86, 92. As well as being freely rotatableabout the spindle 70, the adaptor 90 can axially slide along the spindle70 between the disks 86, 92.

The adaptor comprises a front section 98 and a rear section 100. Thefront section 98 has a first outer diameter, the rear section 100 has asecond larger outer diameter. The two sections allow blades 10 withholes of different diameters to be mounted onto the spindle 70. In FIGS.14 to 18, it can be seen that a blade 10 with a central hole of a firstdiameter is mounted on the rear section 100 of the adaptor 90. In FIG.13, it can be seen that a blade 10 with a central hole of a seconddiameter is mounted on the front section 98 of the adaptor 90.

A spring 102 is sandwiched between the second support disk 86 and aninner shoulder 104 of the adaptor 90. The spring 102 biases the adaptortowards the first support disk 92. A circlip 106 is located around thespindle 70 which limits the maximum extent of axial travel of theadaptor 90. When the adaptor 90 is allowed to slide to its maximumextent and abut against the circlip 106, the rear section 100 is locatedcentrally between the support disks 86, 92.

When a blade 10, having a centre hole with the same diameter of the rearsection 100 of the adaptor is mounted onto the adapter, it fits onto therear section 100 of the adaptor as shown in FIG. 14 to 18. As such, theblade 10 is centrally located between the two support disks 86. 92.However, when a blade 10, having a centre hole with the same diameter ofthe front section 98 of the adaptor is mounted onto the adapter, it fitsonto the front section 98 of the adaptor as shown in FIG. 13. It isprevented from sliding onto the rear section. In order for the blade 10to be secured onto the spindle 70 by the support disks 86, 92, it mustbe located centrally between the two. When the first support disk 92 ismounted onto the spindle 70 after the blade, it pushes the blade 10 andadaptor 90 against the biasing force of the spring 102, moving theadaptor 90 towards the second support disk 86 as shown in FIG. 13. Whenthe blade is securely mounted on the spindle 70, it is centrally locatedbetween the support disks. The front section is similarly mountedcentrally. The adaptor enables two types of blade 10 to be used, itmoving automatically in accordance with blade size.

The pivotal blade guard 22 will now be described.

Referring to FIG. 15, the blade guard 22 is held by being sandwichedbetween two pieces of rubber 108, 110. The blade guard 22 can pivotabout the spindle 70. However, it is frictionally held by the two piecesof rubber 108, 110. In order to pivot the guard 22, the operator mustovercome the friction between the guard 22 and the rubber 108, 110.

A metal bracket 112 is attached to the forward section 8 via four bolts114. The bolts pass freely through the forward section 8 and threadedlyengage with threaded holes formed in the bracket 112. A helical spring116 is sandwiched between the head 118 of each bolt 114 and the forwardsection 8, biasing the bolts 114 out of the holes, pulling the bracket112 towards the forward section. Sandwiched between the bracket and theforward section 8 is a first piece of rubber, 108, the guard 22, asecond piece of rubber 110 to form a rubber-guard-rubber sandwich. Thestrength of the spring 116 determines the amount of frictional forcethere is between the rubber 108, 110 and the guard.

In order to pivot the guard the operator holds the grasp 72 and pivotsthe guard 22 by over coming the frictional force between the guard andthe rubber 108, 110.

The oil and petrol management system will now be described withreference to FIG. 19.

The internal combustion engine is fed with fuel from a carburetor 126.The engine burns the fuel in well known manner to generate rotary motionof its crank shaft 114, which connects to the output shaft 28. Theexhaust gases are then expelled from the engine 24 through an exhaust146 to the surrounding atmosphere.

The power cutter will comprise a petrol tank 124 in which is locatedpetrol for driving the two stroke internal combustion engine 24. Petrolwill pass from the tank 124 via passageway generally indicated by dashedlines 144 through the carburetor 126 which will mix it with air prior tobeing forwarded to the cylinder 118 where it will be burnt. Detail ofthe supply of air, including its filtration will be described in moredetail below. A second tank 128 will also be mounted in the body 2 asshown in which lubricating oil will be contained. The oil will be pumpedout of the tank 128 via an oil pump 130, which is mounted on the crankshaft housing which will be driven via a gear arrangement (not shown)from the crank shaft 114. The oil pump 130, will pump the oil from theoil tank 128 via the pump 130 into the passageway 132 between thecarburetor 126 and the cylinder 120, through the passageways indicatedby dashed lines 142, and then mixing the oil with the air/petrol mixturegenerated by the carburetor 126. It will inject oil at the ratio 1:50 inrelation to the petrol. A sensor 140 will be mounted within thepassageway 132 between the carburetor 126 and cylinder 120. The sensorwill determine whether oil is being pumped correctly in to thepassageway 132 either by checking the pressure of the oil as it entersthe passageway 132 or by detecting the presence of oil in the passageway132. The construction of such sensors are well known and therefore willnot be described in any further detail. The engine will be controlled byan electronic ignition system. The sensor 140 will provide signals tothe electronic ignition system about the oil being pumped into thepassageway 132. In the event that insufficient or no oil is pumped intothe passageway due to the fact that the oil tank is empty or there is ablockage in an oil pipe 142, the sensor 140 will send the signal to theignition system. The ignition system will then either put the engineinto an idle mode or switch the engine off entirely, depending on thesettings of the ignition system. This will ensure that lubricating oilis always added to the petrol in the correct amount prior to combustionwithin the two stroke engine.

The construction of the fuel cap will now be described with reference toFIGS. 20 to 23.

The petrol tank 124 will be mounted within the body of the unit asgenerally indicated in FIG. 19. The tank 124 will be sealed by a fuelcap 13 as shown on FIG. 2.

The fuel cap will comprise an inner cap 202, a clutch 204 and an outercap 206. The inner cap is of a tubular construction with one end 210being sealed. Formed on the inside surface of a side wall 212 is athread 208. When the fuel cap is screwed onto the fuel tank, the thread208 slidingly engages with a thread formed around the external surfaceof the neck of the fuel tank 124.

Located inside the inner cap 202 adjacent the end 210 is a seal 214.When the fuel cap is screwed onto the fuel tank, the seal 214 ensuresthat no fuel can escape from the tank. The inner cap 2 locates withinthe outer cap 206. Sandwiched between the two is the clutch 204. A clip216 locates within a groove 218 of the inner cap and also engages withan inner groove 220 formed within the outer cap. The clip holds theinner cap inside the outer cap whilst allowing it to freely rotatewithin the outer cap 206. The inner cap comprises a number of teeth 222integrally formed with the inner cap. The teeth locate withincorresponding slots 224 formed within the clutch, thus rotation of theinner cap causes rotation of the clutch 204. Formed on the clutch 204are a plurality of resilient arms 226 mounted on the ends of which arepegs 228. The pegs 228 face towards the internal end wall 230 of theouter cap. Formed on the wall are a plurality of ridges 232. The pegs onthe clutch are arranged to co-operate with the ridges 232 in the outercap.

Rotation of the outer cap 206 causes the ridges 232 to engage with thepegs 228 resulting in rotation of the clutch 204, which in turn rotatesthe inner cap 202 via the teeth 222. When the fuel cap is screwed ontothe fuel tank, the inner cap 202 threadingly engages with the neck ofthe fuel tank, the rotation of the inner cap 202 being caused byrotation of the outer cap 6 via an operator rotating it using a fingergrip 234. When the seal 214 located within the inner cap engages withthe end of the neck of the fuel tank, the inner cap 202 is preventedfrom further rotation. This in turn prevents further rotation of theclutch 204. However as the operator continues to exert a rotationalforce on the outer cap 206, the ridges 232 are caused to ride over thepegs 228, the movement of the pegs 228 being allowed by the resilientarms 226 upon which they are mounted. In this way the operator canrotate the outer cap whilst the inner cap remains stationary thuspreventing the operator from over-tightening the fuel cap onto the neckof the fuel tank

The air filtration mechanism for the carburettor 126 will now bedescribed.

The two stroke engine comprises a carburetor 126 which mixes liquid fuelwith air to generate a combustible mixture for powering the engine.However, due to the operation of the power cutter, a large amount ofdust is generated which mixes with the surrounding air. This results indust laden air. In order to ensure that the air entering the carburettoris free from dust it must pass through a filter system to remove thedust.

The filter system will now be described with reference to FIGS. 23 to29.

Inside the body 2 is a filter unit 316 comprising a plastic base 318 andfilter paper 320 folded to form pleats. The filter unit 316 is locatedwithin the body 2 so that the pleats 320 hang vertically downwards whenthe power cutter is in a storage position as shown in FIGS. 1 and 2.

Air will be sucked through the filter system by the carburetor 126. Airenters slots 314 on the rear of the body 2. Air passes (Arrow G) to aspace 322 underneath the filter unit 316 and then passes through thefilter paper 320 to a space 324 above the filter unit 316. Any dustentrained within the air is trapped by the filter unit 316 and heldwithin the pleats of the filter paper 320.

The clean air then passes from the space 324, through a hose 326 to thecarburetor 126 located below the space 322 below the filter unit 316.

In order to enable the operator to remove the dust trapped within thepleats of the filter paper 320, a cleaning device is provided. Thecleaning device comprises a rubber flap 328, mounted on the top of aplastic base 330, a brush 332 attached to the bottom of the plastic base330, a handle 334 attached to the plastic base 330 via to rigid arms338. The base 330 can slide within the space 322 below the filter unit316, widthways across the body 2. Movement is caused by the operatorpulling the handle 334 away from the side of the body 2. Two springs 336bias the handle 334 towards the side of the body 2.

In order to clean the filter unit, the operator pulls the handle 334, tomove the base 330 across the width of the body 2 in the direction ofArrow H, and then releases it to allow it to return in the oppositedirection under the biasing force of the springs 336.

As the base 330 slides across the width, the rubber flap 328 engage withthe pleats 320, as best seen in FIG. 25, knocking the dust of the pleats320. The dust drops to the base 340 of the space 322 below the filterunit 316.

The brush 332 slidingly engages with the base 340 of the space 322. Thebrush 332 brushes the dust to one side or the other, depending on thedirection of movement. An aperture 344 is formed on one side of the body2. As the brush approaches the side of the body, it pushes the dustbeing swept along the base through the apertures, expelling it from thebody 2.

Though FIG. 4 shows the flap 28 moving perpendicularly to the directionof the pleats 320, it will be appreciated by a person skilled in the artthat is possible to rotate the filter paper 320 so that the pleats runin parallel to the sliding movement of the flap 328 as shown in FIG. 26.In such a scenario, the rubber flap 28 may be replaced by a plurality ofbrushes 342.

The construction of the rear handle will now be described with referenceto FIGS. 1 and 2.

The body of the power cutter is constructed in the form of a plasticcasing constructed from a number of plastic clamshell rigidly connectedtogether. The rear clam shell 430 connects to the rear handle 6. Inexisting designs of power cutter, the rear handle 6 is integral with therear clam shell 430. However, if the handle 6 is broken, the whole clamshell 430 needs to be replaced. As handle breakage is common it isdesirable to avoid this.

Therefore, the rear handle 6 in the present invention is constructed asa separate item to that of the rear clam shell 40 (or body 2).

The rear handle 6 is constructed from a separate single clam shell 431which is joined at its top 432 at two points 434 and at its bottom at asingle point 436. Each of the three points 434, 436 is joined using abolt which screws into the plastic clam shell 430. Vibration dampeningmaterial may be used in conjunction with the bolts to reduce the amountof vibration transferred to the handle 6 from the body 2. The use ofsuch vibration dampening material allows limited movement of the handle6 relative to the rear clam 430 at each of the three points. Themovement could be either linear or rotational. One such construction isto surround the bolts with the dampening material in order to sandwichit between the bolts and parts of the clam shell of the rear handle 6.

The top 432 of the handle 6 is in the form of a cross bar. The shape issuch that the bolts fastening the top 432 of the handle to the rear ofthe clam shell 430 are aligned with each other and thus provide a pivotaxis 440 for the rear handle 6 about which it can rotate by a limitedamount.

A person skilled in the art will appreciate that the handle may beconstructed from a number of clam shell connect rigidly together. Rubbersoft grip over mold 442 may also be added to the handle for additionalcomfort.

A second embodiment of an air filtration system will now be describedwith reference to FIG. 30.

The filter device comprises a box 400 in which is mounted filter paper402 which is pleated and which hangs down from the top section frominside the box. A space 404 is formed below the pleat. A large aperture406 is formed in the side of the box below the filter paper and throughwhich a drawer 408 can be slid. The drawer comprises a receptacle 410which locates in the space 404 immediately below the filter paper 402.The drawer 408 can be fastened into place via a screw 412 whichthreadedly engages a threaded hole 414 in the box. Air passes throughslots 314 into the box and into the receptacle 410 in the space 404below the filter paper 402 then through the filter paper 402 into aspace 416 above the filter paper 402 and then exits the space 416 abovethe filter paper through a flexible tube 418 to the carburetor 126. Anydust contained in the air entering the box 400 is blocked by the filterpaper 402.

A combination of two systems have been proposed to shake any dust withinthe filter paper 402 off the filter paper 402 into the drawer 408 sothat the drawer 408 an be removed for emptying.

The first system is very similar to that disclosed in the firstembodiment described above and comprises a rubber flap 420 which isattached to the front end of the drawer 408. As the drawer 408 isinserted into the box 400 the rubber flap 420 engages with the pleatedfilter paper 402. As the drawer 408 slides into the box 400 the rubberflap 420 successively hits the base of each pleat causing any dust onthe pleats to be knocked off and into the drawer 408. As such the actionof inserting or removing the drawer 408 into the box 400 causes dust onthe filter paper 402 to be loosened and allowed to be removed.

The second system relies on the starter cord 422 of the start 12 for thetwo stroke engine 24 of the power saw. When the engine is started, thepower cord 422 needs to be pulled in order to cause it to rotate. As thecord 422 is pulled, it rotates a pulley wheel 424 which causes aneccentric pin 426 to rotate about the axis 428 of the pulley 420. Thiscauses one side of the box 400 to oscillate up and down as indicated byarrows Y. The other side of the box 400 is pivotally attached about anaxis 435 to the body of the power cutter. The reciprocating motion ofthe box 400 causes dust in the filter 402 to be shaken off the filterpaper 402 and into the drawer 408.

Each system cause dust trapped in the filter paper 402 to fail into thedrawer. When the operator first starts up the power cutter, the actionof pulling the starter cord cleans the filter paper 402. Then, theoperator can subsequently clean the filter paper during the operation ofthe power cutter by inserting and removing the drawing 408.

It will be appreciated by a person skilled in the art that the twosystems could be used separately, as well as in combination, a powercutter having only one or the other system.

1. A power cutter comprising: a housing 2; an engine 24 mounted withinthe housing 2; a support arm 7 mounted on the housing and which projectsforward of the housing; a blade mounting mechanism rotatably mounted onthe end of the support arm and which is capable of being rotationallydriven by the engine 24 when the engine is running; a cutting bladehaving a circular central hole and which mounts on and is rotationallydriven by the blade mounting mechanism; a liquid fuel aeration mechanism126 to generate aerated fuel for the engine; an air intake 314 for theprovision of air for the liquid fuel aeration device 126; an airfiltration mechanism 316 to filter the air drawn in from the air intakefor the liquid fuel aeration mechanism; a fuel tank 124 for providingfuel to the liquid fuel aeration mechanism; and an exhaust 146 throughwhich the exhaust gases generated by the operation of the engine areexpelled; wherein the blade mounting mechanism comprises: a spindle 70rotatably mounted on the support arm and which is capable of beingdriven by the engine 24, an adaptor 90 upon which is mounted the cuttingblade, which adaptor is mounted on surrounds the spindle, the adaptor 90having along its length a plurality of radial support surfaces 98; 100which are each concentric with the spindle 70, each having a differentradius; a clamping mechanism 96, 92,86 capable of axially and angularlylocking the cutting blade to the spindle 70; wherein, when the blade 10is mounted on the adaptor 90, the central hole of the blade 10 mounts ona corresponding sized radial support surface 98; 100 of the adaptor 90so that the axis of rotation of the blade 10 is substantially co-axialwith that of the spindle
 70. 2. A power cutter as claimed in claim 1wherein successive radial support surfaces along the adaptor 90 increasein radius.
 3. A power cutter as claimed in claim 2 wherein the cuttingblade is mounted on the adaptor by the radial support surface with thesmallest radius first passes through the central hole of the blade 10followed by successive radial support surfaces of increasing radiusuntil it engages with the corresponding sized radial support surface 98;100.
 4. A power cutter as claimed in any one of the previous claimswherein the adaptor is capable of axially sliding along the spindle. 5.A power cutter as claimed in claim 4 wherein, when the blade is mountedon the adaptor 90, the adaptor is moved by the blade to an axialposition which allows the blade to be mounted on the spindle at the sameaxial position regardless of which radial support surface the blade ismounted upon.
 6. A power cutter as claimed in any one of the previousclaims wherein the adaptor is capable of sliding along the spindle froma first end position to a second end position, there being furtherprovided a biasing force 102 to bias the adaptor 90 to the first endposition.
 7. A power cutter as claimed in claim 6 wherein the blademoves the adaptor against the biasing force.
 8. A power cutter asclaimed in either of claims 6 or 7 wherein the biasing force isgenerated by a helical spring which surrounds the spindle.
 9. A powercutter as claimed in any one of the previous claims wherein the clamplocks the blade 10 in the same axial position on the spindle
 70. 10. Apower cutter as claimed in any one of the previous claims wherein theclamp comprises a first support disk 92 which is non rotatably butaxially slideably mounted on the spindle 70, which engages a first sideof the blade, a second support disk 86 which is non rotatably butaxially slideably mounted on the spindle 70, which engages a second sideof the blade and a flanged nut which, when screwed on to the spindle 70,sandwiches the blade between the first and second support disks.
 11. Apower cutter as claimed in any one of the previous claims wherein theadaptor capable of freely rotating about the spindle